The inactive gas introducing facility described above is used for e.g. introducing an amount of inactive gas into a container accommodating a substrate (such as a semiconductor wafer) for the purpose of restricting unwanted adhesion and accumulation of particles on the substrate thereby to avoid deterioration of the substrate from its proper state due to oxygen and/or humidity.
More particularly, in association with the introduction of inactive gas through the gas feed opening of the container accommodating the substrate, gas present inside the container will be discharged to the outside through a gas discharge opening of the container and the interior of the container will be filled with the introduced inactive gas eventually. Therefore, unwanted adhesion of particles on the substrate and deterioration of the substrate from its proper state due to oxygen and/or humidity are restricted.
Japanese Unexamined Patent Application Publication No. 2006-86308 (Patent Document 1) discloses an example of such inactive gas introducing facility. With this inactive gas introducing facility, nitrogen gas as an inactive gas is introduced at a target feed rate (10 liters/min.) into a pod as a container.
Incidentally, in Patent Document 1, at the gas feed opening, there is mounted a valve configured to allow introduction of nitrogen gas into the container at a pressure slightly higher than the atmospheric pressure. Whereas, at the gas discharge opening, there is mounted a valve configured to allow discharge of the gas inside the container at a pressure slightly higher than the atmospheric pressure.
According to the document, after introduction of nitrogen gas into the container for five minutes, the pod is kept therein with stopping further introduction.
That is, Patent Document 1 describes that at a location separate from a pod shelf storing the pod, there is provided a gas station supporting the pod for the introduction of nitrogen gas and the pod which has received the introduction of nitrogen gas at the gas station is stored on the pod shelf.
Japanese Unexamined Patent Application Publication No. 11-168135 (Patent Document 2) discloses another example of inactive gas introducing facility. With this inactive gas introducing facility, a pod as a container receives feeding of nitrogen gas as an inactive gas for a set feed period. Thereafter, during a set pause period, the feeding of nitrogen gas is paused. Upon lapse of the set pause period, the nitrogen gas is fed again for the set feed period. In this way, nitrogen gas is fed into the pod in an intermittent manner (see e.g. Patent Document 2: paragraphs [0101] through [0118]).
Incidentally, Patent Document 2 describes that nitrogen gas is introduced into the pod which is supported on a shelf of a storage device.
While the document provides no specific explanation regarding the target feed rate used in the feeding of nitrogen gas into the pod, the document describes that in the course of feeding nitrogen gas into the container, when a gas feed valve is opened, the nitrogen gas is fed at a predetermined feed rate as the target feed rate.
Meanwhile, Patent Document 2 also describes that rather than the intermittent feeding of nitrogen gas, the feeding of nitrogen gas into the pod can be carried out in a continuous manner.
With the inactive gas introducing facilities disclosed in Patent Document 1 and Patent Document 2, when inactive gas is fed into the container, the inactive gas is fed at one time at the target feed rate. That is, the feed rate of inactive gas to the container will increase instantaneously or in stepwise to the target feed rate. Therefore, at the time of start of introduction, there will occur vibration in the substrate present inside the container, which vibration leads to dropping off of solvent present on the back face of the substrate. Then, when this dropped solvent adheres to the front face of another substrate which may be present downwardly, the adhesion may invite deterioration of this further substrate from its proper state. Further, at the time of start of introduction, there may occur also floating of particles accumulated on the bottom of the container and these particles may adhere to the substrate.
Incidentally, as an example of the solvent, a developing solution for photoresist processing can be cited.
Incidentally, it is believed that such vibration of substrate and floating of particles inside the container are caused by the phenomenon that the pressure of the gas inside the container first increases sharply and then drops sharply.
That is, in association with the introduction of inactive gas into the container at the target feed rate, there occurs a change in the state of the gas present inside the container from the stationery state to the fluidized state. In this, since the gas inside the container cannot change speedily from the stationery state to the fluidized state, with introduction of inactive gas at the target feed rate all at one, there occurs the phenomenon that the pressure of the gas inside the container first increases sharply and then drops sharply. And, when the pressure of the gas inside the container drops after the sharp rise thereof, there occurs a temporary rapid and drastic flow or turbulent flow of the gas inside the container.
And, with occurrence of the phenomenon that the pressure of the gas inside the container first increases sharply and then drops sharply, vibration may occur in the container, which may cause in turn vibration of the substrate. Also, with occurrence of the temporary rapid and drastic flow or turbulent flow of the gas inside the container, there may occur vibration of the substrate due to the flow of the gas inside the container and/or floating of particles accumulated on the bottom of the container.
Incidentally, such vibration of the substrate and floating of particles accumulated on the bottom of the container will occur more conspicuously when the target feed rate is set to a sufficiently high rate for allowing the interior of the container to reach the condition of being filled with inactive gas within a short period after the start of inactive gas introduction.